Drug loading of polymeric micelles.

PURPOSE: To gain mechanistic insights into drug loading and lyophilization of polymeric micelles. METHODS: PEGylated poly-4-(vinylpyridine) micelles were loaded with dexamethasone. Three different methods were applied and compared: O/W emulsion, direct dialysis, cosolvent evaporation. Micellar dispersions with the highest drug load were lyophilized with varying lyoprotectors: sucrose, trehalose, maltose, a polyvinylpyrrolidine derivative, and ß-cyclodextrin derivatives. For comparison, other PEGylated block copolymer micelles (PEGylated polylactic acid, polylactic acid-co-glycolic acid, polycaprolactone) were freeze-dried. RESULTS: Drug loading via direct dialysis from acetone was a less effective loading method which led to dexamethasone loads <2% w/w. O/W emulsion technique from dichlormethane increased drug load up to ~13% w/w; optimized cosolvent evaporation increased load up to ~19% w/w. An important step for cosolvent evaporation was solubility screen of the drug prior to preparation. Loading was maintained upon lyophilization with ß-cyclodextrins which proved to be versatile stabilizers for other block copolymer micelles. CONCLUSION: Careful solvent selection prior to cosolvent evaporation was a beneficial approach to load hydrophobic drugs into polymeric micelles. Moreover, ß-cyclodextrins could be used as versatile lyoprotectors for these micelles.

Synthesis and Structure-Activity Relationship Studies of C2-Modified Analogs of the Antimycobacterial Natural Product Pyridomycin.

A series of derivatives of the antimycobacterial natural product pyridomycin have been prepared with the C2 side chain attached to the macrocyclic core structure by a C-C single bond, in place of the synthetically more demanding enol ester double bond found in the natural product. Hydrophobic C2 substituents of sufficient size generally provide for potent anti-Mtb activity of these dihydropyridomycins (minimum inhibitory concentration (MIC) values around 2.5 µM), with several analogs thus approaching the activity of natural pyridomycin. Surprisingly, some of these compounds, in contrast to pyridomycin, are insensitive to overexpression of InhA in Mycobacterium tuberculosis (Mtb). This indicates that their anti-Mtb activity does not critically depend on the inhibition of InhA and that their overall mode of action may differ from that of the original natural product lead.

Premature drug release of polymeric micelles and its effects on tumor targeting.

Based on the enhanced permeability and retention (EPR) effect, nanoparticles are believed to accumulate in tumors. In this conjunction, the stability of drug encapsulation is assumed to be sufficient. For clarification purposes, PEGylated poly-(D,L-lactic acid) (PEG-PDLLA) micelles which incorporated the hydrophobic model drug dechloro-4-iodo-fenofibrate (IFF) were investigated. H2N-PEG-PDLLA was synthesized, coupled to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and labeled with 111-indium. From this polymeric species, mixed micelles with H3CO-PEG-PDLLA were prepared which encapsulated the 125-iodine or 131-iodine labeled drug IFF. Bioimaging and biodistribution experiments in healthy and AR42J-tumor bearing mice were carried out to quantify the uptake of the drug and its carrier in single organs. As a result, upon injection of this system, a rapid dissociation of the polymeric carrier and the incorporated drug (<10 min post inj.) was revealed. Regardless of the premature release, the drug showed an enhanced tumor accumulation compared to the polymeric carrier. In conclusion, the self-assembling system allowed for successful solubilization of the hydrophobic drug by physical incorporation into micelles whereas the tumor targeting properties of the drug delivery system could not be sufficiently shown.